1. Field of the Invention
The present invention relates to an fuel injection control apparatus for internal combustion engines, more particularly to an electronic control apparatus for the fuel injection system in which an injector is located before the branching point of intake manifolds to commonly supply the fuel to all or a plurality of cylinders of the internal combustion engine.
2. Description of the Related Art
In the fuel injection system of the internal combustion engine, the amount of the fuel to be injected is extremely reduced upon the deceleration of the engine, or the supply of the fuel is stopped. This is for the purpose of the reduction of hydrogen carbonate in the exhaust gas and the improvement of the fuel consumption rate.
Namely, in the fuel injection system of the type in which the injector is positioned before the branching point of the intake manifolds led to every cylinders, the distance of the manifold between the injector and the respective cylinders becomes relatively long. During the operation of the engine, therefore, the fuel particle atomized by the injector adheres to the inner walls of the manifolds to form a fuel film storage thereon. If, under these conditions, the deceleration begins with the usual fuel control in the operation, almost of the fuel film storage is sucked into a combustion chamber of the engine so that the mixture of the air and fuel becomes temporarily too rich.
In order to avoid the occurrence of the phenomenon stated above, the amount of the fuel to be injected is extremely reduced or the supply of the fuel is stopped, when the engine is decelerated. According to such measures as the reduction or cutting off of the fuel, however, the fuel film storage evaporates so perfectly that the manifold walls become dry.
By the way, as the measures for the transition such as the rapid acceleration, the acceleration enrichment concept is known (cf. SAE Technical Paper Series 800164 "Throttle Body Fuel Injection (TBI)-An Integrated Engine Control System", page 12, right-hand column, first para. "Transient Fuel (Acceleration Enrichment)"). It is stated in this paper that extra fuel is needed for the manifold filling dynamics and the fuel film storage on the manifold walls.
In case, however, the engine is accelerated again immediately after it has been decelerated, the acceleration enrichment under the concept described in this paper is insufficient. That is to say, the degree of dryness of the manifold walls is closely related with the degree or level of the deceleration done precedingly to the acceleration. The greater or higher the degree or level of the deceleration is, the drier the manfold wall becomes. Accordingly, if the deceleration is of very high level, the manifold wall becomes very dry. As a result, upon the succeeding acceleration the greater part of the injected fuel which includes the acceleration enrichment component of the fuel is used only to wet the surface of the inner wall of the manifold, so that the fuel mixture becomes lean. This causes an increase in the contents of noxious components of the exhaust gas, and an acceleration delay.